This invention relates to a process for making a fibrous web having inelastic extensibility.
Japanese Patent Application No. 2001-18315A discloses a process for making a composite sheet having inelastic extensibility. This process generally comprises the steps of placing a first web made of thermoplastic synthetic fibers and inelastically extensible in one direction upon at least one surface of a second web made of a thermoplastic synthetic resin and elastically extensible in the one direction and bonding the. first web to the second web intermittently in the one direction. These first and second webs bonded to each other in this manner are stretched together in the one direction without exceeding the elastic limit of the second web as well as the breaking extension of the first web. Then the second web is left to contract under its elasticity and thereupon the composite sheet having a predetermined elastic extensibility is obtained. The composite sheet obtained in this manner is appropriately bulky and has a soft touch because the composite sheet contracts after the component fibers of the first web have been stretched and permanently set. In this way, this composite sheet can be used as a suitable stock material for the disposable wearing article such as a disposable diaper or a disposable gown.
In order to ensure that the step of stretching the first web gives the above-cited composite sheet of prior art the appropriate bulkiness desired for a stock material used in the wearing article, the first web is stretched preferably by 50-400%, more preferably by 70-200% and then contracted preferably 100-70% under a contractile force of the second web. To ensure the soft touch essential to a stock material for the wearing article, fibers having a small diameter, for example, of 20 μm or less is preferably used as the component fibers of the first web and such fibers are stretched preferably by 70-200%. However, depending on the component fibers of the first web, stretching of the component fibers of the first web at this ratio may cause fiber breakage in many of the component fibers and the resultant composite sheet may exhibit fuzz due to the fiber breakage. Such fuzz may often deteriorate luster and soft touch desired for this composite sheet. This inconvenience is due to the fact that, in the course of melt spinning these fibers, high draft exerted on the fibers promotes orientation of the polymer molecules constituting the fibers and such orientation restricts the extensibility of the fibers. Even if the fibers have a relatively high extensibility, the orientation will result in a high stretch stress of the fibers and a correspondingly large force will be necessary to stretch the first web. In other words, such first web can not be easily stretched.